Abstract: Glutathione and glutathione peroxidase activity are important components in the complex body defense against oxidative damage. In this study, we have measured malondialdehyde (MDA) as a marker of oxidative stress, the antioxidant glutathione (GSH), and activity of the antioxidant enzyme (GSHPx), in a cohort of free-living elderly subjects from the Belfast Elderly Longitudinal Free-living Aging STudy (BELFAST), hypothesizing that free-living Senieur-approximated nonagenarians might demonstrate enhanced antioxidant defense mechanisms. The main finding in the BELFAST octo/nonagenarians was that plasma antioxidant glutathione increased in nonagenarian compared with septo/octogenarian subjects (P= .015), whereas conversely antioxidant glutathione peroxidase activity fell in the nonagenarian group (P < .0001). In the same subject group, malondialdehyde, a measure of lipid peroxidation, showed no change across the age groups (P= .73). These results might overall represent a situation in which elderly survivors in the BELFAST study have evolved a sort of free radical/antioxidant equilibrium as a mechanism of successful aging.